1. Field of the Invention
The present invention relates to an optical modulator capable of modulating light pixel by pixel in accordance with a picture signal and enabling an image to be displayed. More particularly, the invention relates to an optical modulator which can perform color display by using only a single panel and an image projection display apparatus using the optical modulator.
2. Description of the Related Art
An image display system using an optical modulator such as a liquid crystal device takes the form of not only a direct vision display but also an image projection display apparatus such as a liquid crystal projector for performing display by projecting an image on a screen. The image projection display apparatus displays a color image by leading three colored rays used for color display to pixels corresponding to the respective colors of the optical modulator, modulating the light in accordance with a picture signal, and projecting the resultant light onto a screen. Image projection display apparatus each using a liquid crystal display device (hereinbelow, referred to as a liquid crystal panel) as an optical modulator are broadly divided into two types; a single-panel type constructed by using a single liquid crystal panel having color separating means for separating light to colored rays of red (R), green (G), and blue (B), and a triple-panel type constructed by using three liquid crystal panels in total having no color separating means arranged in respective paths of the colored rays of R, G, and B.
Since the triple-panel type display needs three liquid crystal panels for R, G, and B, the costs are high. Besides the liquid crystal panels for the respective colors, relatively large sized prism, mirror, and the like for synthesizing images of the colors formed by using the panels are necessary. Consequently, a vein space is produced in the system and it is accordingly difficult to make the system compact. It is not easy to adjust positions and angles of the three liquid crystal panels at the time of arrangement. Further, even if one of the three liquid crystal panels has an uneven gap (unevenness in thickness of a liquid crystal layer), brightness unevenness occurs in a synthesized image displayed which causes color irregularity. It is therefore necessary to strictly keep the gap uniform with respect to all of the liquid crystal panels, so that it is difficult to manufacture the triple-panel type display system.
For this reason, recently, attention is being paid to the single-panel type image projection display apparatus. The single-panel type image projection display apparatus separates light emitted from a white light source into rays of three primary colors of red, green, and blue by color separating means provided on the liquid crystal panel, allows the colored rays to enter pixels (liquid crystal cells) for the respective colors which are regularly arranged, spatially modulates the incident colored rays in accordance with respective picture signals, and transmits and outputs the resultant light. As the color separating means in this case, a color filter or the like is conventionally used. Although the display using the color filter has a simple structure and can be easily made small and light at low costs, on the other hand, since the heat generating amount by light absorption of the color filter is large, it is difficult to achieve high brightness. In this case, since it is indispensable to sufficiently cool the liquid crystal panel, the construction is complicated and the size is large.
For dealing with the problem, a single-panel type color liquid crystal display system which can perform color display without using a color filter (hereinbelow, referred to as a color-filterless single-panel type color liquid crystal display system) has been proposed in, for example, Japanese Patent Application Laid-open No. 4-60538 or "Asia Display '95, p887". In the system, a condenser microlens is disposed facing every three pixels. Three colored rays of B, R, and G are allowed to enter each microlens from mutually different directions and condensed. The outgoing rays from the microlens are allowed to enter pixels corresponding to the three colors of B, R, and G. Since a color filter is not employed, just a small amount of light is absorbed and light entering a region between pixels (i.e., a black matrix region in which a switching device for driving pixels is formed) can be also effectively utilized. The substantial aperture ratio is therefore increased and the brightness level is accordingly increased. The aperture ratio denotes the ratio of the total area of display pixels to the effective display area.
In the above-mentioned color-filterless single-panel type display system, however, since a transmission type liquid crystal panel is used, the display pixel area (almost equal to the part occupied by the pixel electrodes) and the black matrix area are not permitted to overlap one another. Consequently, the existence of the black matrix area reduces the aperture ratio and hinders realization of high brightness after all.
Since the transmission type liquid crystal panel is used in the conventional color-filterless single-panel type color liquid crystal display system using the microlenses, it is difficult to further improve the aperture ratio.